The Bodys Defense System Chapter 31 Phagocytosis Lymphocytes

The Body’s Defense System Chapter 31 Phagocytosis Lymphocytes

The Germ Theory of Diseases that are caused by pathogens are known as infectious diseases. Pathogens include certain bacteria, protozoans, fungi, and worms, and viruses. In the mid 1800’s, Louis Pasteur demonstrated the importance of microorganisms.

Joseph Lister, an English surgeon, reduced infections in patients by washing hands and sterilizing equipment. Lister hypothesized that microorganisms caused infections that was killing 50% of his patients following surgery.

Koch’s Postulates Robert Koch, a German physician, built upon the previous work of Pasteur and Lister. His method is used to identify the pathogens that cause specific diseases.

Modern life has evolved in a world of microbes. Some are symbiotic and benefit metabolism but others are pathogenic TERMITES (Reticulitermes flavipes) Nitrogen fixing bacteria in the roots of legumes Anthrax spores Enemy Within: Bacteria video

Viruses are “non-living” without a host. A protein coat and nucleic acids Virus video

Diversity of animal viruses Measles

Influenza Viruses 1918 Flu Epidemic Infectious disease video

The Body’s Defense 1. Nonspecific defense against infection a. Barriers external and internal b. Phagocytic cells, complement proteins c. Inflammatory response 2. Specific defense (immune system)

First line of defense: Barriers 1. Intact skin: secretions create a p. H of 3 -5 2. Mucous membranes 3. Tears, saliva contain antimicrobial proteins 4. Digestive system contains acids 5. Ciliated cells in trachea with mucous traps microbes prevents them from entering lungs Lining of trachea shows mucous producing cells and ciliated cells

Second line of defense: Phagocytic Leukocytes (WBC) 1. Neutrophils 60 -70% of all WBC short-lived phagocytes 2. Monocytes 5%, develop into macrophages 3. Basophils involved in the inflammatory response 4. Eosinophils involved in parasitic invaders 5. Natural killer cells destroy viral infected body cells

Nonspecific defense Monocytes give rise to Macrophages Phagocytosis by macrophage The scanning electron micrograph above, shows a human macrophage (gray) approaching a chain of Streptococcus pyogenes (yellow). Riding atop the macrophage is a spherical lymphocyte.

Inflammatory Response • During an inflammatory response, chemical signals trigger changes in blood vessels and attract white blood cells that help destroy the invaders • Histamines are released by basophils and mast Increased blood flow • Chemokines attract WBC • Increased Phagocytic activity

Specialized Proteins Infected cells produce interferon, which stimulates noninfected cells to manufacture substances that block virus reproduction. This limits the spread of virus to neighboring cells.

The Third Line: Targeted Defense is specific immunity provided by Lymphocytes Antigens are the foreign molecules that elicits a specific response B and T lymphocytes have specific antigen receptors

Development of Lymphocytes B cells are produced in bone and make antibodies T cells are produced in thymus and are known for the cellular response Helper T Cells Cytotoxic T Cells Both cells produce memory cells that give “permanent” immunity

Pathway to specific immunity involves recognizing self from non-self. Macrophages or infected cells present antigens (non-self molecules) to the lymphocytes. Lymphocytes are specific to the antigens • B cells produce antibodies • Cytotoxic T cells kill infected body cells • Helper T cells stimulate other cells and defenses

Pathway of a specific response to antigens Macrophages engulf and then display the antigens of pathogens they have "eaten. " This display activates a specific version of helper T cells. The activated helper T cells in turn stimulate cytotoxic T cells and B cells.

Macrophage and T cells interact to stimulate Helper T cells Cytotoxic T cells B cells CD 4 is one of the receptor sites used by HIV virus.

Cytotoxic T cells attack and destroy infected body cells

B Lymphocytes are selected by specific antigens (foreign particles). Specific selection results in the cloning of the B cells and production of antibodies that “match” the antigen.

Antibodies secreted by the B cells bind to antigens that have a complementary or matching shape.

Antibodies have lots of different shapes that have the potential to bind to antigens.

Antibodies interact with antigens and aid in elimination several ways.

T Dependent Response Follow the steps that stimulate the production of antibodies

Overview of the Immune Response

Primary and Secondary Immune Responses The first exposure to a pathogen produces B and T memory cells specific to that pathogen. A second exposure activates those memory cells.

Vaccinations provide long term immunity. A vaccine stimulates the production of antibodies and memory cells that protect against future exposure to the pathogen.

The introduction of the measles vaccine in the early 1960 s helped to greatly reduce the number of reported cases of measles.

Immunity can occur naturally or artificially 1. Active Immunity: stimulates the infected person’s immune system, generally considered permanent a. Immunization by vaccination give the person a weakened, dead, fragment of the pathogen b. Recover from the infection

2. Passive Immunity: person receives antibodies only so it is temporary a. Maternal immunity occurs when antibodies pass from mother to baby through placenta and breast milk b. Artificial injection of antibodies gives short term immunity Defending the Body Against Disease video

Immune System Failures Allergies: immune reaction involving histamines to a “harmless”allergen. Autoimmune diseases: immune system destroys body cells, type I diabetes, multiple sclerosis, rheumatoid arthritis AIDS: Acquired Immune Deficiency Disease Beta cells normally synthesize the insulin Closer Look at Some Diseases video

Allergy: abnormal immune system sensitivity to an otherwise harmless antigen An allergic reaction releases histamines, which cause the characteristic allergy symptoms. These symptoms may include a runny nose and watery eyes.